Air raid alarm device



Jan. 7, 1961 M. DE FEO 2,968,801

AIR RAID ALARM DEVICE Filed March 17, 1959 MICHHEL DE FEO INVENTOR.

BY .j.a6a%

Patent 149w:

United States Patent AER RAID ALARM DEVICE Michael De Fee, 128 Dewitt St., New Haven, Conn.

Filed Mar. 17, 1959, Ser. No. 799,911

1 Claim. (Cl. 340-416) My invention relates to alarm devices actuated by a predetermined change of the normal frequency of the alternating current electrical supply, and more particularly to emergency alarm devices applicable in civil defense warning systems for alerting the public in case of air raids and other emergencies.

One of the important objects of my invention is to provide an alarm device which can be actuated by a very small predetermined change in the frequency of the electrical supply, provided however, that this changed fre quency is maintained for a predetermined period. Consequently, the change in the frequency of the electrical supply required for the actuation of my alarm device will not disturb the normal operation of the apparatus and appliances connected to the electrical supply, also, accidental transient changes in the frequency of the electrical supply will not actuate my alarm device.

Another important object of my invention is to provide an alarm device which cannot be actuated or affected by the voltage fluctuations experienced in electrical networks, or by the transient voltage surges caused by lightning, or by switching.

A further object of my invention is to provide an alarm device which has reliable operation, unaffected by eX- treme temperature changes, sympathetic vibrations or accidental jarring, which is economical in first cost and durable in service.

Other objects and advantages of my invention will be apparent during the course of the following description.

In the accompanying drawing, forming a part of the present application, wherein for the purpose of illustration is shown a preferred form of my invention, the figure is a diagrammatic view of my alarm device.

Referring to the drawing, the numerals 1 and 2 desigmate the terminals of an alternating current electric supply, having a normal frequency, which is maintained constant between very close limits under normal operating conditions. In the present example this normal frequency is assumed to be 60 cycles per second.

Operatively connected to this alternating current electric supply is the frequency impulse integrator 3, a relay of novel characteristics, composed of the following principal elements: The solenoid 5 connected across the terminals 1 and 2, and receiving constant excitation from the alternating current electric supply. The magnetic core 4, preferably made of iron laminations, with its central portions surrounded by the solenoid 5, forming a magnetic circuit interrupted by a considerable air space above the solenoid 5. Disposed in this air space of the magnetic circuit is the vibrator arm 7, having a stationary end 6, electrically connected to the terminal 2, and a free end 8 provided with a contact. In the form of my invention illustrated the stationary end 6 of the vibrator 7 is secured to the magnetic core 4 with an insulating element interposed; in alternative forms the support of the stationary end 6 of the arm 7 may be different.

It is fundamental in the present invention that the vibrator arm 7 is so constructed that it has a predetermined natural frequency of vibration, designated as the alarm frequency, which is different from the normal frequency of the electric supply. Experience shows that a difference as small as one cycle per second is sufficient to actuate my alarm device under any operating conditions, which means that the changing of the frequency of the electric supply network from the normal frequency to the alarm frequency will not impair or disturb the normal operation of the apparatus and appliances connected into the network. Another important characteristic of the vibrator arm 7 is that it has a large maximum amplitude of vibration which can be reached only if the impulses of the magnetic field of the core 4 and solenoid 5 are maintained at the alarm frequency for a considerable period, which means that accidental transient variations of the operating frequency of the electric supply cannot actuate my alarm device, neither the transient voltage surges experienced in electric networks due to lightning and switching.

In the example illustrated and described the vibrator arm 7 is made of resilient steel, annealed adjacent to its free end, to reduce the remanent magnetism. In alternative forms of my invention other magnetic materials may be applied.

The numeral 9 designates the stationary contact, which is so positioned that the contact of the free end 8 will reach it only at the maximum amplitude of oscillation of the vibrator arm 7. Connected between the stationary contact 9 and the terminal 1 are the resistor 10 and the neon light bulb 12, which latter is an important element of the present invention. The function of this neon light bulb is to produce light when a predetermined amount of electric energy is transmitted by the contact of the vibrator arm 7. In alternative forms of my invention this function may be accomplished by light bulbs containing other gaseous material than neon which will produce light when a predetermined amount of electric energy is transmitted to it.

The numerals 12 and 13 represent the terminals of a direct current electric supply, which may be provided by means of a rectifier or other known methods. Connected across these terminals 12 and 13 are the photo electric element 14, the resistors 15 and 16, and the solenoid of the relay 17. The photo electric element 14 is an essential element of my invention; it is located adjacent to the light bulb 11, exposed to the light produced by the bulb l1 and has the function to pass a current through the solenoid of the relay 17, when actuated by the light produced by the bulb ll, thereby causing the closing of the contacts of the relay 17. These contacts of the relay 17 are inserted in a circuit, in series with the alarm element 18, connected to the alternating current terminals 1 and 2, and the alarm element is so constructed as to give an audible signal when the contacts of the relay 17 are closed. The alarm element 18 may be constructed as to give visible signals, when energized.

The operation of my alarm device is as follows: In view of the difference between the normal frequency of the electric supply and the natural frequency of the vibrator arm 7, the mechanical impulses of the magnetic field, set up by the solenoid 5 at normal frequency will 'have alternately positive and negative effect on the vibration of the arm 7, so that the energy accumulated will not be sufficient to reach the maximum amplitude of the vibration of the arm 7. Consequently, at normal frequency, or at any other frequency differing from the alarm frequency, the vibrator arm 7 will not develop sufl'icient amplitude of vibration to reach the stationary contact 9 to actuate my alarm device.

When, however, the supply frequency is changed to the value of the alarm frequency, the magnetic impulses being synchronized with the natural vibration frequency o he 7, the amplitude of the vibration of the arm 7 dually increase, and if this condition will be maintamed" for a sufiiciently long. period of time, the free end 8 of; the arm 7 will reach the stationary contact 9, there by transmitting a' current through the neon light bulb 11. zlf tliese currentv impulses are repeated for a suflicient period of .tirne, .the energy imparted to the light bulb 11 will produce sufiicient light to actuate the photo electric element 14, so as to energize the relay 17 and thereby actuate the alarm element.

Thus, my invention operates on a novel principle, that instead of merely detecting the presence of the predetermined alarm frequency, it integrates its efiect, so that no actuation can take place unless the alarm frequency is sustained for a predetermined length of time.

It is to be understood that the form of my invention herein described and illustrated, is only an example of the same, and that various changes in the material and the arrangement of the parts may be resorted to, without departing from the spirit of my invention or the scope of the subjoined claim.

I claim:

. An alarm device comprising, an alternating current electric supply of normal frequency, having terminals; a solenoid operatively connected to said alternating current electric supply; an iron core interrupted by an air space, forming a magnetic circuit surrounded and magnetized by said solenoid; a vibrator arm, of resilient magnetic r material, disposed in said air space of said magnetic circuit, and having a stationary end connected to one of the terminals of the alternating current electric supply, and a free end provided with a contact, said arm having a natural frequency of vibration equal to a predetermined alarm frequency and is constructed to assume a predetermined maximum amplitude of vibration when exposed r I 4 to the impulsesof said magnetic circuit at alarm frequency for a predetermined length of time; a stationary contact so located as to be impacted by the contact of the free end of said vibrator arm at said maximum amplitude of vibration, permitting the flow of alternating current through said vibrato-r arm into said stationary contact; a neon light bulb connected to said stationary contact and to the other terminal of the alternating current electric supply, producing light when receiving a predetermined amount of electrical energy through said vibrator arm; a direct current electric supply, having terminals; a photoelectric element, connected to one of thet terminals of said direct current supply, and located adjacent to said neon bulb, permitting the flow of direct current when exposed to the light produced by said neon bulb; a relay comprising a solenoid connected to said photo-electric element and to the other terminal of said direct current supply, and a switch connected to one of the terminals of the alternating current supply, said switch assuming a closed position when said solenoid is energized and an open position when said solenoid is deenergized; an alarm, element connected between said switch and the other terminal of said alternating current supply, producing an alarm signal when said switch is closed.

References Cited in the file of this patent UNITED STATES PATENTS 2,371,192 Short Mar. 13, 1945 2,388,530 'Deal Nov. 6, 1945 2,709,801 Sprague May 31, 1955 2,799,853 Colwell et al. July 16, 1957 2,811,712 Saunders Oct. 29, 1957 2,867,795 Longton et a1 Jan. 6, 1959 2,909,668 Thurlby et al. Oct. 20, 1959 

